We present here a pH-responsive activatable aptamer probe for targeted cancer imaging based on i-motif-driven conformation alteration. This pH-responsive activatable aptamer probe is composed of two single-stranded DNA. One was used for target recognition, containing a central, target specific aptamer sequence at the 3＇-end and an extension sequence at the 5＇-end with 5-carboxytetramethylrhodamine （TAMRA） label （denoted as strand A）. The other （strand ｜）, being competent to work on the formation of i-motif structure, contained four stretches of the cytosine （C） rich domain and was labeled with a Black Hole Quencher 2 （BHQ2） at the 3＇-end. At neutral or slightly alkaline pH, strand ｜ was hybridized to the extension sequence of strand A to form a double-stranded DNA probe, termed i-motif-based activatable aptamer probe （I-AAP）. Because of proximity- induced energy transfer, the I-AAP was in a ＂signal off＇ state. The slightly acidic pH enforced the strand I to form an intramo- lecular i-motif and then initiated the dehybridization of I-AAP, leading to fluorescence readout in the target recognition. As a demonstration, AS1411 aptamer was used for MCF-7 cells imaging. It was displayed that the I-AAP could be carried out for target cancer cells imaging after being activated in slightly acidic environment. The applicability of I-AAP for tumor tissues imaging has been also investigated by using the isolated MCF-7 tumor tissues. These results implied the I-AAP strategy is promising as a novel approach for cancer imaging.
利用作为肿瘤细胞识别分子的核酸适配体(Aptamer)的高特异性和高亲和力以及作为信号报告单元的近红外量子点(QDs)的高荧光发射强度和低生物背景干扰特性,构建了一种基于Aptamer功能化近红外QDs的新型纳米荧光探针,并进一步结合流式细胞术在单细胞荧光分析方面的高通量、简便和快速等优势,建立了一种检测白血病细胞的新方法.以基于Cell-SELEX(Cell-based systematic evolution of ligands by exponential enrichment)技术针对CCRF-CEM人急性白血病细胞筛选的特异性Aptamer Sgc8c为模型,构建了Sgc8c-QDs探针,其仅需与细胞样品培育30 min即可实现对缓冲液和血清中靶细胞的简单、快速和高特异性检测.与传统荧光染料标记技术相比,该方法不仅大大提高了分析灵敏度,还显示出对血清等复杂生物样品的高适用性和优良检测性能.鉴于Cell-SELEX技术在其它白血病细胞Aptamer筛选领域的应用潜力,该方法有望作为一种通用技术在白血病诊断及预后监测等方面发挥重要作用.
